Abstract: :
Purpose: The electroretinogram (ERG) waveform of young zebrafishin response to short–wavelength stimuli (320–480nm) consists of a large voltage–negative potential atstimulus onset followed later by a voltage–positive b–wave,while the ERG to long–wavelength stimuli (500–640nm) consists primarily of a voltage–positive b–waveto stimulus onset. This study examined the nature of this wavelength–dependentvoltage–negative response in young zebrafish. Methods:ERGs were obtained from light–adapted young (6–21days postfertilization) and adult (1 year or older) zebrafish(Danio rerio) to 200 ms flashes of various wavelengths and irradiances.Log irradiance versus response amplitude functions of the ERGresponse at various post–stimulus–onset times (e.g.,50, 75 & 150 ms following stimulus onset) were derived aswell as spectral sensitivity functions. Aspartate, and a combinationof APB (DL–2–amino–4–phosphonobutyricacid) and PDA (cis–2,3–piperidinedicarboxylic acid),were applied to the eye to suppress the responses of varioustypes of retinal neurons, leaving primarily photoreceptor activity.Results: In adults, the irradiance vs. response function slopeswere positive regardless of stimulus wavelength and post–stimulus–onsettime. In young zebrafish, the slopes of the irradiance vs. responsefunctions were negative to short–wavelength stimuli atshort post–stimulus–onset times (i.e., 75 ms followingstimulus onset), and positive at longer post–stimulus–onsettimes (e.g., 150 ms following stimulus onset). The slopes ofthe functions to long–wavelength stimuli were positiveat all post–stimulus–onset times. Aspartate eliminatedvoltage–positive responses; the irradiance vs. responsefunction slopes were negative regardless of stimulus wavelengthand post–stimulus–onset times. In addition, thesefunctions were similar to the functions of normal young fishto short–wavelength stimuli at short post–stimulus–onsettimes. APB combined with PDA produced results similar to aspartate.Spectral sensitivity derived from aspartate–exposed subjectsat various post–stimulus–onset times were similar.Conclusions: The initial voltage–negative response ofyoung zebrafish to short–wavelength stimuli appears tobe due to photoreceptor activity. ERG waveform differences acrossstimulus wavelengths suggest that the circuitry of ultraviolet–and short–wavelength cone types is different from thatof middle– and long–wavelength cone types in zebrafish.